Electrical attachment device

ABSTRACT

Electrical attachment device such as a speaker device and a microphone device requiring an electric power for use with a tape recorder having an earphone jack, a remote switch jack and a microphone jack for extension connection of the electrical attachment device. The electrical attachment device has plugs mating with the jacks of the tape recorder, the polarity of the connection of the center terminal and the shield terminal of the plug for connection to the remote switch jack is reversed with respect to that of the center terminal and the shield terminal of the plug for connection to the earphone jack or the microphone jack so that the electric power is supplied to the attachment device from the tape recorder when the plugs are coupled with the respective jacks thereby dispensing with an additional electric source for the attachment device.

United States Patent 1191 FOREIGN PATENTS OR APPLICATIONS Germany 179/1PC Sato July 3, 1973 1 ELECTRICAL ATTACHMENT DEVICE PrimaryExaminer-Kathleen l-l. Claffy 75 I t M ki Sat T k .l 1 men or 0 yo apanAssistant Examiner-Jon Bradford Leaheey [73] Assignee: Olympus OpticalCo., Ltd., Anomey-Kelman & Berman Shibuya-ku, Tokyo, Japan [22] Filed:Nov. 19, 1971 [57] ABSTRACT [21] Appl. No.: 200,366 Electricalattachment device such as a speaker device and a microphone devicerequiring an electric power 52 us. c1. .1 mm PC use with? 'ecmder P aremote switch ack and a microphone ack for exten- [51] Int. Cl H011-3/00 f h l l h d 7 58 Field of Search 179/1 sw, 1 PC, 1 A, e eectllca 9The electrical attachment device has plugs matmg w1th 179/1 DD, 339/148,154

the acks of the tape recorder, the polarity of the con- 56] ReferencesCited nection of the center terminal and the shield terminal of the plugfor connection to the remote switch ack is UNITED STATES PATENTSreversed with respect to that of the center terminal and 2,929,8773/1960 Irick 179/1 A th hi ld terminal of the plug for connection to the3,300,585 1/1967 F QY earphone jack or the microphone jack so that theelecg g g g 2 tric power is supplied to the attachment device from 2 1 341 the tape recorder when the plugs are coupled with the 31015I7001/1962 semen III: I. 179/1 PC respective Jacks thereby dispensing withan additimal electric source for the attachment device.

12 Claims, 28 Drawing Figures 7 Sheets-Sheet I INVENTOR Has a a, (lSovfo Patented July 3, 1973 3,743,784

7 Shea ts-Sheet 3 INVENT Nanak! 6 O Patented July 3, 1973 7 3,743,784

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MMM Who 2 ACa/WS Patented July 3, 1973 3,743,784

7 Sheets-Sheet 5 INVENTOR Mas -kl Swfo Aa /v TS Patented July 3, 19733,743,784

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K ma/ amp M ELECTRICAL ATTACHMENT DEVICE BACKGROUND OF THE INVENTION Thepresent invention relates to an electric attachment device such as aspeaker, a microphone, a frequency-modulated tuner which itself requiresan electric power for the operation thereof and is adapted to bedetachably attached to an electric appliance such as a tape recorderwhich is provided with an electric source so that the electric power issupplied to the attachment device from the electric appliance when theformer is attached to the latter.

A miniature tape recorder has been made very small in size and a speakerand an output circuit of the ampli fier thereof have been eliminatedfrom the main body of the tape recorder, and an earphone adapted to beconnected to the tape recorder through an earphone jack has been usedfor minimizing the size of the tape recorder. Thus, when it is desiredto use a speaker, an output circuit and a speaker are connected to thetape recorder through the earphone jack so that the output signal of thetape recorder is supplied to the speaker through the output circuit toamplify the output signal. In this case, an electric source is requiredfor the output circuit thereby necessitating the casing of the outputcircuit to be enlarged for housing a battery therein. Further, it isnecessary to cut off the electric source from the output circuit eachtime the operation of the output circuit is terminated so thatmanipulation of the tape recorder is made troublesome. Alternatively,the electric power for the output circuit may be supplied from the taperecorder. To this end, however, it is necessary to provide separateterminals in the tape recorder for supplying the electric power to theoutput circuit so that the construction and the manipulation of the taperecorder are made complicated and troublesome.

The input impedance of a microphone circuit of a tape recorder having anamplifier incorporating a transistor is several kiloohms at the highest.Therefore, a dynamic type or a magnetic type microphone having animpedance of the value near that of the input impedance of themicrophone circuit of the tape recorder has been used with the taperecorder of the type described above.

Recently, a condenser microphone or a ceramic microphone which is verysmall in size and inexpensive in price has been developed. The condensermicrophone has characteristics that the lower region in frequency is cutoff when the impedance thereof is made low. Therefore, it is desirableto connect an active element such as a field effect transistor (referredto hereinafter as FET) having a high input impedance and a low outputimpedance between the condenser microphone and the amplifier of the taperecorder so as to achieve a low input impedance of about severalkiloohms to be supplied to the amplifier of the tape recorder while thecondenser microphone is actuated at a high performance without cuttingoff the lower region in frequency caused by the low impedance thereof.

When a condenser microphone is used with the microphone circuit of thetape recorder of the type described above, no serious problems arise ifthe condenser microphone is housed in the main body of the taperecorder. However, when the condenser microphone is used as a remotemicrophone for a tape recorder by connecting it to the tape recorderthrough a micropone jack thereof, the tape recorder must be de signed tohave a special construction so that the condenser microphone can beconnected to the tape recorder without deteriorating the performancethereof, thereby making it impossible to use the condenser microphonewith a conventional tape recorder as a remote microphone, so that theuse of the condenser microphone is made inconvenient.

It is, therefore, desirable to permit the condenser microphone to beused commonly with any conventional tape recorder by the provision of anFET so that the output impedance of the condenser microphone is reducedby the FET to one to several kiloohms suitable for supplying to theamplifier of the tape recorder having the input impedance of severalkiloohms. Further, it is desirable to locate the FET adjacent to themicrophone so as to prevent the oscillation thereof.

To this end, it is advantageous to arrange the condenser microphone andthe FET in a common casing so that the low output impedance of the FETis supplied to the amplifier of the tape recorder while the condensermicrophone is actuated at a high performance and the oscillation ispositively prevented.

In this case, an electric source is required for the FET. To this end, asmall size silver or mercury cell may be incorporated in the casing ofthe microphone. However, this requires an extra electric source althoughit can be of very little capacity. Further, it is desirable to cut offthe electric source each time the operation of the microphone isterminated thereby making the manipulation of the tape recordertroublesome. Alternatively, the electric power for the FET may besupplied from the electric source of the tape recorder. In this case,however, it is necessary to provide separate terminals in the taperecorder for connecting the FET to the tape recorder so as to supply theelectric power to the FET from the tape recorder, thereby resulting in acomplicated construction of the tape recorder while the manipulation ofthe tape recorder is made troublesome.

In case the electric power for the FET arranged in the casing of thecondenser microphone is supplied from the main body of the taperecorder, electric noise of the electric source of the tape recordermight cause oscillation of the microphone circuit. It is, therefore,necessary to provide a decoupling circuit including a capaci tor and aresistor which is connected to the electric source so that theoscillation is positively prevented. It is, however, disadvantageous tolocate such a decoupling circuit in the main body of the tape recorder,because the resistor of the decoupling circuit is connected at all timesin series to the load of the tape recorder.

On the other hand, if the capacitor and the resistor forming thedecoupling circuit are arranged in the easing of the microphone, anextra space is required thereby resulting in increase in the size of thecasing. This is a fatal defect for a miniature microphone.

Further, in order to carry out a secret recording, it is necessary toremotely operate the tape recorder while it is held in a pocket, forexample, of the clothes of the operator, thus requiring a remote switchfor operating the tape recorder.

In the recording operation of a tape recorder, a microphone is usuallyused. In this case, the recording necessarily contains not only thenecessary sound desired to be recorded but also unwanted sound existingin the ambient atmosphere thereby deteriorating the quality of therecording.

Therefore, when the recording is to be carried out in a lecture meeting,for example, where the electric signal generated by the microphone of alecturer is transmitted by a frequency-modulated transmitter (referredto hereinafter as FM transmitter) through an antenna, it is desirable toeffect the recording by connecting a frequency-modulated tuner (referredto hereinafter as FM tuner) to the microphone jack of the tape recorderso as to receive by the FM tuner the electric signal transmitted fromthe FM transmitter so that the lecture is recorded without accompanyingany unwanted noise existing in the ambient atmosphere in the lecturemeeting. In this case, however, an electric source is required for theFM tuner. No serious problems arise if a battery is arranged in thecasing of the FM tuner, except that an extra space is required in thecasing for locating the battery therein while the manipulation of thetape recorder is made troublesome, because the electric source must becut off each time the operation of the tape recorder is terminated.

Alternatively, the electric power may be supplied to the FM tuner fromthe main body of the tape recorder. In this case, however, separateterminals are required in the tape recorder so that the electric poweris supplied from the tape recorder to the FM tuner. This makes theconstruction of the tape recorder complicated and the FM tuner can notbe used with a conventional tape recorder having no such terminals.

In carrying out a secret recording, the size of various attachmentdevice to be connected to the main body of the tape recorder which iskept in a pocket, for example, of the clothes of the operator must beminimized so as to conveniently arranged in the clothes of-the operatorfor operation of the tape recorder without being noticed by otherpersons.

The present invention aims at solving the above described problems ofthe prior art electric appliances.

SUMMARY OF THE INVENTION An object of the present invention is toprovide a novel and useful electrical attachment device requiring anelectric power for the operation thereof and adapted to be detachablyconnected to an electric appliance such as a tape recorder having anelectric source, wherein the electric power is supplied to theattachment device from the electric appliance by merely connecting theformer to the latter for the operation thereof without requiring anyfurther connecting means for supplying the electric power from theelectric appliance to the attachment device.

Another object is to provide a novel and useful speaker deviceconnectable to a tape recorder having an electric source, wherein theelectric power required for the operation of the speaker device issuppliedthereto from the tape recorder by merely connecting the speakerdevice to the tape recorder for the operation thereof without requiringany additional connecting means in the tape recorder for supplying theelectric power from the tape recorder to the speaker device.

A further object of the present invention is to provide a novel anduseful microphone device connectable to a tape recorder having anelectric source, wherein the electric power required for the operationof the microphone device is supplied thereto from the tape recorder bymerely connecting the microphone device to the tape recorder for theoperation thereof without requir-' ing any additional connecting meansin the tape recorder for supplying the electric power from the taperecorder to the microphone device.

A still further object of the present invention is to provide a noveland useful microphone device of the type described above, wherein theoscillation of the microphone device due to possible electric noise ofthe electric source of the tape recorder is positively prevented whilethe remote control of the operation of the tape recorder is effected bythe microphone device thereby facilitating the operation of the taperecorder.

Another object is to provide a novel and useful FM tuner deviceconnectable to a tape recorder having an electric source, wherein theelectric power required for the operation of the FM tuner is suppliedthereto from the tape recorder by merely connecting the FM tuner to thetape recorder for the operation of the FM tuner without requiring anyadditional connecting means in the tape recorder while the requiredrecording of an information transmitted from an FM transmitter iseffecting without containing any unwanted noise existing in the ambientatmosphere around the tape recorder.

A further object is to provide a novel and useful microphone deviceconnectable to a tape recorder, which is small in size for facilitatingthe operation thereof while the oscillation of the microphone device dueto possible electric noise of the electric source of the tape recorderis positively prevented.

Another object of the present invention is to provide a novel and usefulultraminiature microphone device for use with a tape recorder, which isarranged in a necktie pin so that it is advantageously used in a secretrecording.

A still further object is to provide a novel and useful microphonedevice for use with a tape recorder, wherein the electric source of themicrophone device is connected in the circuit thereof only when themicrophone device is connected to the tape recorder thereby minimizingthe consumption of the electric source.

In accordance with the present invention, the above object is achievedby the provision of a speaker device comprising a loudspeaker connectedto an output circuit for amplifying the electric signal supplied from atape recorder connected thereto, the tape recorder having an electricsource, an earphone jack and a remote switch jack, the speaker devicebeing provided with a pair of plugs adapted to be connected to theremote switch jack and the earphone jack of the tape recorder,respectively, for cooperation of the speaker device with the taperecorder, thereby permitting the electric power required for theoperation of the speaker device to be supplied thereto from the taperecorder by the mere connection of the pair of plugs of the speakerdevice to the jacks of the tape recorder for the operation of thespeaker device.

In accordance with another feature of the present invention, themicrophone device is adapted to be con-- nected to a tape recorderhaving an electric source, an amplifier incorporating a transistor, aremote switch jack and a microphone jack, the microphone device beingprovided with a condenser microphone, an active element such as an FETfor accommodating the output impedance of the microphone device to theinput impedance of the amplifier of the tape recorder and a pair ofplugs adapted to be connected to the remote switch jack and themicrophone jack of the tape recorder, respectively, for the cooperatingof the microphone device with the tape recorder, thereby permitting theelectric power required for the operation of the FET of the microphonedevice to be supplied thereto from the tape recorder by the mereconnection of the pair of plugs of the microphone device to the jacks ofthe tape recorder for the operation of the microphone device.

In accordance with the other feature of the present invention, themicrophone device is provided with a decoupling circuit and a remoteswitch so that the oscillation of the microphone device due to thepossible electric noise of the electric source of the tape recorder ispositively prevented while the remote control of the operation of thetape recorder is made possible by the remote switch of the microphonedevice thereby facilitating the operation of the tape recorder.

In accordance with a still further feature of the present invention, theFM tuner is adapted to be connected to a tape recorder having anelectric source, an amplifier, a remote switch jack and a microphonejack, the FM tuner being provided with a pair of plugs adapted to beconnected to the remote switch jack and the microphone jack of the taperecorder, respectively, for cooperation of the FM tuner with the taperecorder while the electric power required for the operation of the FMtuner is supplied thereto from the tape recorder by the mere connectionof the pair of plugs to the jacks of the tape recorder for the operationof the FM tuner, thereby permitting the required recording of aninformation transmitted from an FM transmitter to be carried out by thetape recorder without accompanying any unwanted noise existing in theambient atmosphere around the tape recorder.

In accordance with the other feature of the present invention, themicrophone device is provided with a condenser microphone, a mating FETarranged in the same casing as that of the condenser microphones foraccommodating the output impedance of the microphone device to the inputimpedance of a tape recorder to be used with the microphone device whilepreventing the oscillation thereof, and an electric source for the FET,the tape recorder being provided with a microphone jack whilethe'microphone device is provided with a plug engageable with themicrophone jack for the connection thereof with the tape recorder, theelectric source for the FET being arranged in the plug therebyminimizing the size of the microphone device.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a block diagram showing thearrangement of the microphone with a remote switch and an earphoneconnectable to a conventional tape recorder;

FIG. 2 is a block diagram similar to that of FIG. 1 but showing theelectric circuit of the speaker in the tape recorder constructed inaccordance with the present invention, in which the electric power forthe speaker is supplied from the tape recorder through the remote switchjack thereof;

FIG. 3 is a block diagram similar to FIG. 2 but showing the modificationof the electric circuit of FIG. 2;

FIG. 4 is a block diagram showing the electric circuit of the microphonein the tape recorder of the present invention in which the electricpower for the microphone is supplied from the-tape recorder through theremote switch jack thereof as in the case of the speaker shown in FIG. 2or 3;

FIG. 5 is a block diagram showing the modified circuit of the microphonehaving a remote switch of the tape recorder constructed in accordancewith the present invention;

FIG. 6 is a schematic general view showing the appearance of themicrophone of FIG. 5;

FIG. 7 is a block diagram showing another form of the circuit of themicrophone having a remote switch of the tape recorder of the presentinvention;

FIG. 8 is a schematic general view showing the appearance of themicrophone of FIG. 7;

FIG. 9 is a block diagram showing the circuit of the FM tuner for usewith the tape recorder constructed in accordance with the presentinvention;

FIG. 10 is a wiring diagram showing another form of the microphone ofthe present invention;

FIG. 11 is a schematic general view showing the appearance of themicrophone plug constructed in accordance with the present invention;

FIG. 12 is a sectional view taken along line AA in FIG. 1 1 showing theinternal arrangement of the microphone plug of FIG. 11;

FIG. 13 is a sectional view taken along line 8-8 in FIG. 12 showing theinternal arrangment of the microphone plug of FIG. 12;

FIG. 14 isla general view showing the appearance of the other embodimentof th microphone plug of th present invention;

FIG. 15 is a sectional view taken along line CC in FIG. 14 showing theinterior of the microphone plug of FIG. 14;

FIG. 16 is a wiring diagram showing the electric circuit of a furtherembodiment of the microphone of the present invention;

FIG. 17 is a perspective view showing the necktie pin in which themicrophone of FIG. 16 is incorporated;

FIG. 18 is a longitudinal sectional view showing the internalarrangement of the necktie pin of FIG. 17;

FIG. 19 is a perspective view showing a modified form of the microphoneof FIG. 17 which is incorpo' rated in a necktie pin;

FIG. 20 is a wiring diagram showing the electric circuit of the otherform of the microphone of the present invention;

FIG. 21 is a perspective view showing a necktie pin in which themicrophone of FIG. 20 is incorporated;

FIG. 22 is a longitudinal sectional view showing the interior of. thenecktie pin of FIG. 21;

FIG. 23 is a wiring diagram showing a further modification of theelectric circuit of the microphone of the present invention;

FIG. 24 is a perspective view showing the appearance of the microphoneplug used in the microhone of FIG. 23;

FIG. 25 is an enlarged sectional view showing the interior of themicrophone plug of FIG. 24;

FIG. 26 is a wiring diagram showing the switching circuit of the taperecorder constructed in accordance with the present invention;

FIG. 27 is a perspective view showing the modified form of themicrophone plug used in the switching circuit of FIG. 26; and

FIG. 28 is a sectional view showing the interior of the microphone plugof FIG. 27.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Referring to FIG. 1showing a conventional tape recorder, the tape recorder compriseselectric source I, amplifier unit 2, motor 3 and main switch 4 connectedto the plus terminal of the electric source 1. As shown, remote switchjack 5 is connected between the main switch 4, the amplifier unit 2 andthe motor 3 and microphone jack 6 is connected between the inputterminal of the amplifier unit 2 and the earth. Microphone unit 7 isprovided with a remote switch connected to the remote switch plug 8adapted to be connected to the remote switch jack 5, the remote switch10 being connected between the shield terminal and the center terminalof the remote switch plug 8. The microphone unit 7 incorporates thereina microphone 12 and a matching transformer 11 having the primary windingconnected to the microphone 12 as shown. The terminals of the secondarywinding of the matching transformer 11 are connected to the shieldterminal and the center terminal of microphone plug 9 mating with themicrophone jack 6, respectively. Earphone is connected to the shieldterminal and the center terminal of earphone plug 14, respectively,which is adapted to be connected to the earphone jack 13 of the taperecorder.

In such a tape recorder of the conventional type, when plug 9 of themicrophone unit 7 is connected to the microphone jack 6 of the taperecorder and the remote switch plug 8 is connected to the remote switchI to the electric circuit of the remote switch so that,

when the main switch 4 is closed, the tape recorder can be switched toON or OFF by operating the remote switch 10. Earphone 15 can be operatedby connecting the plug 14 thereof to the earphone jack 13. If it isdesired to actuate a speaker, an output circuit and the speaker areconnected to the earphone jack 13 so as to supply the output to thespeaker after amplified by the output circuit. In this case, a separateelectric source is required to energize the output circuit.

FIG. 2 shows the electric circuit of the present invention, in which theoutput circuit and the speaker can be operated without requiring anyseparate electric source by utilizing the remote switch jack 5 and theearphone jack 13 of the tape recorder.

' In FIG. 2, the speaker comprises an output circuit 21 1 for amplifyingthe output signal from the amplifier unit 2 of the tape recorder and-aspeaker 22 adapted to be energized by the output circuit 21. The pluslead wire of the output circuit 21 is connected to the shield terminalof the plug 23 mating with the remote switch jack 5 and the shieldterminal of the plug 23 is connected to the center terminal of the plug23, while the earth lead wire of the output circuit 21 is connected tothe shield terminal of the plug 24 mating with the earphone jack l3 andthe center terminal of the plug 24 is connected to the input terminal ofthe output circuit 21.

By the arrangement shown in FIG. 2, when the plug 23 is connected to theremote switch jack 5 and the plug 24 is connected to the earphone jack13, the plus side of the electric power for the output circuit 21 isapplied thereto t'rom the tape recorder through the plug 23, jack 5,while the earth side of the electric power is supplied to the outputcircuit 21 through the plug 24, jack l3.

A switch 25 may be provided between the center terminal and the shieldterminal of the plug 23 as shown in FIG. 3 instead of directlyshort-circuiting the center terminal and the shield terminal of the plug23. In this case, the switch 25 serves as the remote switch of thespeaker circuit.

FIG. 4 shows a microphone circuit in which a condenser microphone havingan FET is used by utilizing the remote switch jack 5 and the microphonejack 6 as shown in FIG. 1.

In FIG. 4, the condenser microphone unit 31 has a condenser microphone32 and an FET 33. The gate of the FET 33 is connected to the condensermicrophone 32, while the drain of the FET 33 is connected to the shieldterminal of plug 34 similar to the plug 8 in FIG. 1 and the source ofthe FET 33 is connected through a resistor to the shield terminal ofplug 35 which is similar to the plug 9 in FIG. 1. Remote switch 36 isconnected between the shield terminal and the center terminal of theplug 34.

By the arrangement shown in FIG. 4, when the plug 34 is connected to theremote switch jack 5 and the plug 35 is connected to the microphone jack6 of the conventional tape recorder, the plus side of the electric powerfor the FET 33-is applied thereto from the tape recorder through theplug 34, jack 5 while the earth side of the electric power is applied tothe FET 33 through the plug 35, jack 6. The remote switch 36 may bedispensed with and the shield terminal and the center terminal of theplug 34 may be short-circuited' in order to make the device compact.

FIG. 5 shows a microphone circuit having a decoupling circuitincorporated in the remote switch in accordance with the presentinvention for preventing the oscillation of the microphone circuit, inwhich the earphone circuit is omitted although it may be incorporated,and FIG. 6 shows the appearance of the microphone of FIG. 5.

In FIG. 5, the tape recorder is similar to that shown in FIG. 4 exceptthat the earphone circuit is omitted, and the condenser microphonecircuit is substantially similar to that shown in FIG. 4 except that theremote switch 36 is dispensed with. A remote switch housing 41 isprovided between the microphone unit3l and the plugs 34 and 35 whichincorporates therein a remote switch 42 connected between the shieldterminal and the center terminal of the plug 34. A capacitor C and aresistor R are provided in the remote switch housing 41, and thecapacitor C is connected between the drain of the FET 33 and thecondenser microphone 32 as shown while the resistor R is connectedbetween the drain of the FET 33 and the remote switch 42, so that thecapacitor C and the resistor R form the decoupling circuit.

By the arrangment of FIG. 5, the microphone unit can be made compact,because the decoupling circuit is arranged in the remote switch housinginstead of the microphone unit. I

FIG. 7 shows a modification of the microphone unit of FIG. 5 while FIG.8 shows the appearance of the microphone unit of FIG. 7.

As is clear from the drawings, lead wires extend separately from theplugs 34 and 35, the lead wires from the plug 35 being connected to themicrophone unit 31 while the remote switch housing 41 is connected tothe lead wires from the plug 34, so that the remote switch housing 41 isarranged separately of the microphone unit 31.

FIG. 9 shows the electric circuit of the present invention in which theFM tuner is coupled with the tape recorder with-out requiring anyseparate electric source for the FM tuner by utilizing the remote switchjack and the microphone jack of the tape recorder.

In FIG. 9, the tape recorder per se is similar to that shown in FIG. 5.The FM transmitter unit for use with the FM tuner shown in FIG. 9comprises a microphone 51 for a lecturer in a lecture meeting, forexample, a transmitter 52 connected to the microphone 51, an electricsource 53 connected to the transmitter 52 for the energization thereof.An antenna 54 is connected to the transmitter 52 so that the auralsignal received by the microphone 51 is amplified and frequencymodulated so as to be transmitted from the antenna 54. FM tuner unitcomprises a FM tuner 55 and an antenna 56 connected thereto. The FMtuner 55 has plugs 57 and 58 which are adapted to be connected to theremote switch jack and the microphone jack 6 of the tape recorder. Theplug side of the output of the FM tuner 55 is connected to the centerterminal of the plug 57 and the center terminal is connected to theshield terminal of the plug 57 while the earth side is connected to theshield terminal of the plug 58, the center terminal thereof beingconnected to the output terminal of the FM tuner 55. Thus, the FM tunerunit receives the frequency modulated aural signal through the antenna56 and demodulates the same by the FM tuner 55.

In operation, when the plug 57 is connected to the remote switch jack 5and the plug 58 is connected to the microphone jack 6 of the taperecorder; the plus side of the electric power for the FM tuner 55 isapplied from the electric source 1 of the tape recorder through the plug57, jack 5 and the earth side is applied through the plug 58 and thejack 6, while the motor 3 and the amplifier unit 2 of the tape recorderare energized by the electric source 1 through the jack 5 and the plug57.

If it can be seen when the antenna 56 of the FM tuner 55 receives theinput signal from the antenna 54 of the transmitter unit as in the caseof the recording in a lecture meeting, it suffices to merely connect theplugs 57, 58 of the FM tuner 55 to the respective jacks 5 and 6 of thetape recorder in order to carry out the recording by the tape recorder.

In case, however, when it can not be noticed when the input signal isapplied to the antenna 56 of the FM tuner 55, it is necessary tomaintain the tuner 55 to be connected to the tape recorder so as to keepthem in operative position, thereby consuming the electric power as wellas the tape in the tape recorder. In such a case, it is preferred toprovide in the tape recorder a switching circuit or a voice startingcircuit which is adapted to commence the operation of the electriccircuit for the motor 3 when an aural signal is applied thereto. In thiscase, the motor 3 will not be driven even though the main switch 4 iskept closed, unless the aural signal is applied to the switchingcircuit, the electric power to be consumed being reduced to that for theFM tuner 55 and the amplifier unit 2, while the tape recorder is kept ininoperative position. When an aural input signal is applied to the FMtuner 55, then the motor 3 commences its rotation by the switchingcircuit provided in the tape recorder for the recording operation of thetape recorder so that the waste of the tape is kept to the minimum.

FIG. 10 shows the alternative form of the electric circuit of themicrophone device of the present invention for use with the conventionaltape recorder, in which a condenser microphone and an FET are in thesame casing and the FET is energized by an electric source housed in themicrophone plug of the microphone device thereby making it possible tominimize the size of the microphone device so as to be suitable for asecret recording while the high impedance output of the FET is suppliedto the microphone and the low impedance output of the tape recorder isaccommodated for the supply to the microphone by the provision of theFET.

In FIG. 10, the circuit of the microphone device is substantiallysimilar to that of FIG. 4 except that the remote switch 36 of FIG. 4 isomitted and the drain of the FET 33 is connected to the shield terminalof the microphone plug 66 through lead wire 87 and an electric source 67such as a mercury cell or a silver cell or the like having a relativelylow capacity and one terminal of the microphone 32 opposite to thatconnected to the gate of the FET 33 is connected to the shield terminalof the plug 66 through lead wire 86 while the source of the FET 33 isconnected to the center terminal of the plug 66 through lead wire 88,the lead wires 86, 87, 88 forming together an electric cord 64.

The electric source 67 is housed in the body 68 of the plug 66 made ofnon-conductive plastic material.

The detailed construction of the body 68 of the microphone plug 66 isshown in FIGS. 11 to 13. In the drawings, the plug 66 and the cord 64extend from the body 68 to one side of which a cover 63 for the electricsource 67 is detachably secured. The plug 66 consists of an inner shaftand an outer tube 76 surrounding the inner shaft 75, isolating rings 77,78 being interposed between the shaft 75 and the tube 76 at therespective ends thereof so as to electrically isolate the shaft 75 fromthe tube 76. A leaf spring 80 serving as a negative pole of the electriccell 79 housed in the recess of the body 68 is secured to theinnersurface of the cover 63 so as to contact with the negative pole of thecell 79. Casing 81 of electrically conducting material is provided inthe recess of the body 68 and the positive pole of the cell 79 contactswith an electrically conducting pin 82 serving as a positive pole whichis secured to the casing 81. The casing 81 is electrically connected tothe outer tube 76 while the innershaft 75 is connected to a terminalplate 85 which is electrically isolated from the casing 81 as well asthe cell 79 by a spirally wound isolating strip 84.

The pin 82 is electrically connected to the lead wire 87 and the casing81 is connected to the lead wire 86 while the terminal plate 85 isconnected to the lead wire 88, the lead wires 86, 87, 88 extending inthe cord The microphone device shown in FIGS. 11 13 can be made verysmall in size thereby permitting it to be conveniently used in a secretrecording when used with a miniature tape recorder.

FIGS. 14 and 15 show another form of the microphone plug of the presentinvention in which a standard type cylindrical electric cell is housed.As shown, the body 92 of the plug is made by the molding of electricallynon-conductive plastic material. Electrically conductive cylindricalcasing 99 is located in the body 92 and the flange 76a formed in theouter tube 76' of the plug is threadedly secured to the casing 99 whichis electrically connected to the lead wire 104 similar to lead wire 86in FIG. 10. An electrically non-conductive plate 102 is secured to theopen end of the casing 99 adjacent to the plug and electricallyconducting layers 102a 102b are provided on the respective side of theplate 102, the layer 102a contacting with the casing 99 while the layerl02b is electrically isolated therefrom. The layer 102 has a contact 103secured thereto which contacts with the negative pole of the cell 98.The inner shaft 75 of the plug is in contact with the layer 102b and thelayer l02b is connected to the lead wire 106 similar to lead wire 88 inFIG. 10. An insulating plate 100 is secured to the other end of thecasing 99 and an electrically conductive leaf spring 101 is secured tothe plate 100 which is connected to the lead wire 105 similar to thelead wire 87 in FIG. 10. The leaf spring 101 contacts with the positivepole of the cell 98.

The cell 79 or the cell 98 shown in FIG. 12 or FIG. 15 can be exchangedby removing the cover 63 in FIG. 12 or detaching the outer tube 76 inFIG. 15 together with the inner shaft 75.

In the embodiments shown in FIGS. 10 to 15, since the microphone 32 andthe FET 33 are arranged in the same casing closely to each other, thepossible oscillation is positively prevented, and, further, the size ofthe microphone per se can be made to the minimum, because the electricsource is housed in the body of the microphone plug.

FIGS. 16 to 18 show another form of a microphone device of the presentinvention which is extremely compact so as to be conveniently used in asecret recording.

The electric circuit shown in FIG. 16 is substantially similar to thatshown in FIG. 10 except that the electric cell 67' is arrangedseparately from the body of the plug 68.

In FIGS. 17 and 18, the microphone casing 115 housing therein themicrophone 32 and the FET 33 is provided with a decoration pattern 119and a voice transmitting opening 120, and the casing 115 is fixedlysecured to the front side of the body 121 of a necktie pin having adecoration 122 in its front side with the pattern 119 and the opening120 being faced outwardly.

An L-shaped lug 123 is provided in the rear side of the necktie pin anda circularly wound portion 123a is formed in the free end of the lug 123in which a pivot shaft 124 is located. The clipper portion 125 of thenecktie pin is pivotally mounted on the shaft 124 and a spring 126 isarranged about the shaft 124 so as to urge the clipper portion 125against the body 121 of the necktie pin.

The cell 67' is housed in a case 127 (indicated schematically as 31a inFIG. 16) and the case 127 is fixedly secured to the rear side of theclipper portion 125. A leaf spring 129 contacting with the negative poleof the cell 67' is fixed to the inner surface of the cover 128. Acontact 130 contacting with the positive pole of the cell 67 is providedin the case 127, an insulating ring 131 being interposed between thecontact 130 and the clipper portion 125 and the case 127. Lead wires133, 134 of the cord-64' and a lead wire (not shown) are connected tothe microphone 32, the FET 33 and the cell 67, respectively, so as tomake the electrical connection as shown in FIG. 16.

FIG. 19 shows a modification of FIG. 17, in which the microphone casing115 and the case 127 are incorporated in a necktie pin having the body135 and the clipper portion 136 integral with the body 135. In thisembodiment, the electrical connection between the cord 64 and themicrophone, the FET and the electric cell is made by lead wires (notshown) in accordance with FIG. 16.

The necktie pin per se may be made of a metal so as to be used as anelectric conductor for the minus side of the electric current, therebymaking the construction simple. v

In the embodiments shown in FIGS. 16 19, the size of the microphonedevice is made to the minimum to facilitate the secret recording bysimply attaching the necktie pin to the necktie of the operator whilethe oscillation is positively prevented as described previously.

FIGS. 20 22 show a further embodiment of the microphone device of thepresent invention. 1

The electric circuit of FIG. 20 is substantially similar to that shownin FIG. 10 except that the microphone 32 is housed in a separate casing31". Thus, the electric source 67 is housed in the body 68 of the plug66.

As shown in FIG. 22, the casing 31" of the condenser microphone 32 isattached to the outer surface of the body 141 of the necktie pin byfitting a portion of the casing 31" within the opening 142 of the body141 so as to reduce the height of the casing 31". A decoration plate 143covers the outer surface of the body 141 as well as the casing 31" withthe voice transmitting hole 144 of the plate 143 being in alignment withthe microphone 32 in the casing 32". A circularly wound portion 146 isformed in the tip of U-shaped extension of the body 141, in which thepivot shaft 124 is secured. The clipper portion 148 is pivotably mountedon the shaft 124 and a spring 126 is located around the shaft 124 so asto urge the clipper portion 148 toward the body 141.

The clipper portion 148 is in the U-form in the crosssection so as toprovide a space therein, in which a base plate 149 mounting thereon theFET 33 and other elements is secured, a cover 150 being provided tocover the elements on the base plate 149. Thus, the casing 31 in FIG. 20is formed by the clipper portion 148 and the cover 150.

The microphone 32 and the FET 33 and other elements are electricallyconnected by high quality shielding wires 151 so as to make theelectrical connection shown in FIG. 20, thereby preventing the electricoscillation of the microphone device. It is preferred to form theclipper portion 148 and the cover 150 by a metal having a high shieldingeffect.

The cord 64 is elastically held to the clipper portion 148 by an elasticholder 152 made of rubber or plastic material. posi-tion The FET 33 andother elements may be arranged in a separate shielding case which issecured in the rear side of the clipper portion 148.

Since the microphone device can be used without being covered by anyportion of the clothes of the operator, a high quality recording isinsured during the secret recording operation of the tape recorder.

FIGS. 23 25 show a still further embodiment of the microphone device ofthe present invention. The circuit shown in FIG. 23 is substantiallysimilar to that shown in FIG. 10 except that the electric cell 67" ishoused in the same casing as that in which the microphone 32 and the FET33 are housed anda microswitch 157is arranged between the shieldterminal of the plug 66 and the minus terminal of the electric cell 67"through lead wire 175, the lead wires 170, 171 and 172 extending in thecord 169 corresponding to the lead wires 86, 88 and 87 of FIG. 10.

FIGS. 24 and 25 show the construction of the body 68" of the plug 66 inwhich the switch 157 is arranged.

In the figures, the switch 157 has an elastically movable actuatingmember 160 at the tip of which an annular portion 161 is formed throughwhich the plug 66 loosely extends.

In FIG. 25, the chassis 164 of the tape recorder is provided with a jack162 which is secured to the chassis 164 by means of a nut 163. The innershaft 75 and the outer tube 76 serving as the center terminal and theshield terminal, respectively, are electrically insulated by insulatingrings 77, 78 as in the previous examples. The microswitch 157 isembedded in the body 68" of the plug so that the actuating member 160thereof extends downwardly from the body 68" as shown. The plug 66 perse is embedded at its one end beneath the switch 157.

The lead wire 170 from the cord 169 is connected to the outer tube 76 ofthe plug 66 and the-lead wire 171 is connected to the inner shaft 75,while the lead wire 172 is connected to one terminal 173 of the switch157, the other terminal 174 of the switch 157 being connected to theouter tube 76 being connected by the lead wire 175, so that theelectrical connection makes the electric circuit of FIG. 23.

In operation, when the plug 66 is inserted into the jack 162, theactuating member 160 of the switch 157 is engaged with the exposed endsurface of the jack 162 so as to be moved to close the switch 157. Whenthe plug 66 is withdrawn from the jack 162, the actuating member 160returns to its natural position by its resiliency, so that the switch157 is automatically opened, thereby saving the consumption of theelectric power.

FIGS. 26 to 28 show the other embodiment of the microphone device of thepresent invention.

The electric circuit of FIG. 26 is like that shown in FIG. 4 but theswitch 36 of FIG. 4 is omitted and, instead, the drain of the FET 33 isconnected to the center terminal of the plug 179 mating with the remoteswitch jack through an electric cell 67" while the shield terminal ofthe plug 179 is connected to the shield terminal of the plug 66 matingwith the microphone jack 6 of the tape recorder, the earphone jack 13 ofFIG. 4 being omitted in FIG. 26. The lead wires 192, 193 and 194 extendtogether to form the cord 169. The electric cell 67" 71 is of arelatively small capacity such as a silver cell or a mercury cell,because it is used only for energizing the FET 33 which serves toimpedance change for the micrphone 32.

FIG. 28 shows the construction of the body 185 of the plug 66 shown inFIG. 27 in which the remote switch plug 179 is incorporated and which iscoupled with the tape recorder.

In FIG. 28, the microphone plug 66 is similar to that shown in FIG. 25.A jack 162 mating with the plug 66 issecured to the chassis 164 of thetape recorder by a nut 163 while a remote switch jack 5 is located inthe chassis 164 of the tape recorder.

The remote switch plug 179 comprises an inner shaft 183 having aninsulating piece 184 attached to its outer end while an insulating tube184' surrounds the other end of the shaft 183 and an electricallyconductive outer tube 186 is provided around the insulating tube 184'.

The jack 5 has an insulating base plate 187 fixed to the chassis 164. Anelectrically conductive tube 188 for engaging with the inner shaft 183of the plug 179 is secured to the base plate 187. An elastically movableswitching piece 189 is secured to the base plate 187. The embracingportions 190, 191 of the switching piece 189 are adapted to be fittedwith the outer tube 186 while the other end of the piece 189 isresiliently urged toward the base plate 187 so that the tube 188contacts with the other end of the piece 189.

The lead wire 192 is connected to the outer tube 76 and the lead wire193 is connected to the inner shaft while the lead wire 194 is connectedto the inner shaft 183, the outer tube 76 of the plug 66 being connectedto the outer tube 186 of the plug 179 by the lead wire 204. Thus, whenthe plug body is coupled with the tape recorder, electrical connectionis made between the inner shaft 183, the tube 188, the switching piece189, the embracing portions 190, 191 and the outer tube 186 so that theelectric cell 67" is made operable, i.e., the electric power is suppliedfrom the cell 67" to the FET 33 by utilizing the remote switch jack 5only when the plug body 185 is coupled with the tape recorder.

In case a low impedance microphone other than a condenser microphone isused, the electric source for the FET is not required, thus making itpossible to use the conventional remote control system. In this case,the length of the inner shaft 183 or the insulating tube 184 is enlargedso that it urges the switching piece 189 so as to disengage it from thetube 188 to open the circuit of the electric cell 67 The construction ofthe jack 5 is not limited to the above described arrangement but may bemodified variously.

It is preferred to mold the portion of each of the plugs 66 and 179 andthe lead wires integral with the body 185.

The above described construction may be utilized when an extensionspeaker device having a speaker, an amplifier and an electric source isused with a miniature tape recorder having no speaker and an outputamplifier incorporated therein and adapted to use an earphoneconnectable thereto so as to save the consumption of the electric power.

1 claim:

1. In a speaker device for use with a tape recorder having an earphonejack and a remote switch jack for extension connection to an earphoneand a remote switch, respectively, said speaker device including aspeaker connected to an output circuit therefor, the improvement whereinsaid speaker device comprises a first and a second plug adapted to becoupled with said remote switch jack and said earphone jack,respectively, the shield terminal of said first plug being connected tothe plus side of said output circuit as well as to the center terminalof said first plug, while the earth side of said output circuit isconnected to the shield terminal of said second plug, the centerterminal thereof being connected to the input terminal of said outputcircuit, thereby permitting electric power for said output circuit to besupplied from a power source in the tape recorder when said first andsaid second plug are coupled with the respective jacks for the operationof the tape recorder.

2. In a speaker device for use with a'tape recorder having an earphonejack and a remote switch jack for extension connection to an earphoneand a remote switch, respectively, said speaker device including aspeaker connected to an output circuit therefor, the improvement whereinsaid speaker device comprises a first and a second plug adapted to becoupled with said remote switch jack and said earphone jack,respectively, the shield terminal of said first plug being connected tothe plus side of said output circuit, while the earth side of saidoutput circuit is connected to the shield terminal of said second plug,the center terminal thereof being connected to the input terminal ofsaid output circuit, a remote switch being connected between the centerterminal and the shield terminal of said first plug, thereby permittingelectric power for said output circuit to be supplied from a powersource in the tape recorder when said first and said second plug arecoupled with respective jacks for the operation of the tape recorderwhile remote control is effected by said remote switch.

3. In a microphone device for use with a tape recorder having a remoteswitch jack and a microphone switch jack, said microphone deviceincluding a high impedance microphone and a field effect transistor formatching the impedance with the tape recorder, the improvement whereinsaid microphone device comprises a first and a second plug adapted to becoupled with said remote switch jack and said microphone jack,respectively, the gate of said field effect transistor being connectedto said microphone while the drain is connected to the shield terminalof said first plug and the source is connected to the center terminal ofsaid second plug, the shield terminal thereof being connected to saidmicrophone, a remote switch being connected between the center terminaland the shield terminal of said first plug, thereby permitting electricpower for said field effect transistor to be supplied from a powersource in the tape recorder when said first and said second plug arecoupled with the respective jacks for the operation of the tape recorderwhile remote control is effected by said remote switch.

4. Microphone device according to claim 3, further comprising adecoupling circuit arranged in the lead wires connecting said plugs tosaid microphone and said field effect transistor, said remote switchbeing physically located in a common housing with said decouplingcircuit.

5. Microphone device according to claim 3, further comprising adecoupling circuit arranged integral with said remote switch, saiddecoupling circuit and said remote switch being connected between thelead wires lead from said microphone and said field effect transistorand from said plugs separately from the lead wires connecting directlysaid second plug to said microphone as well as said field effecttransistor.

6. In an FM tuner device for use with a tape recorder having remoteswitch jack and a microphone jack for recording the signal transmittedfrom a FM transmitter, said FM tuner device including an FM tuner and anantenna connected to said FM tuner, the improvement wherein said FMtuner device comprises a first and a second plug adapted to be coupledwith said remote switch jack and said microphone jack, respectively, theplus side of said FM tuner being connected to the center terminal ofsaid first plug which is connected to the shield terminal thereof, whilethe earth side of said FM tuner is connected to the shield terminal ofsaid second plug, the center terminal thereof being connected to theoutput terminal of said FM tuner, thereby permitting the electric powerfor said FM tuner to be supplied from the tape recorder when said firstand second plugs are coupled with the respective jacks of the taperecorder operation thereof.

7. FM tuner device according to claim 6, wherein the tape recorder has aswitching circuit and is operable only when said FM tuner receives thesignal from the FM transmitter, while said FM tuner is kept in operableposition by coupling said first and second plugs with the respectivejacks.

8. In a microphone device for use with a tape recorder having amicrophone jack, said microphone device including a condensermicrophone, a field effect transistor for accommodating the impedance ofthe tape recorder with said microphone and an electric source for saidfield effect transistor, the improvement wherein said microphone devicecomprises a plug adapted to be coupled with said microphone jack andsaid electric source is housed in the body of said plug, the centerterminal of said plug being connected to the source of said field effecttransistor the shield terminal of which is connected to one terminal ofsaid microphone, the other terminal thereof being connected to the gateof said'field effect transistor, the plus terminal of said electricsource being connected to the drain of said field effect transistorwhile the minus terminal of said electric source is connected to theshield terminal of said plug, thereby minimizing the size of saidmicrophone device while oscillation thereof is positively prevented.

9. Ina microphone device for use with a tape recorder having amicrophone jack, said microphone device including a condensermicrophone, a field effect transistor for accommodating the impedance ofthe tape recorder with said microphone and an electric source for saidfield effect transistor, the improvement wherein said microphone devicecomprises a normally opened micro-switch and a plug adapted to becoupled with said microphone device, the center terminal of said plugbeing connected to the source of said field effect transistor the gateof which is connected to one terminal of said microphone, the otherterminal thereof being connected to the shield terminal of said plug,the plug terminal of said electric source being connected to the drainof said field effect transistor, while the minus terminal of saidelectric source is connected to one contact of said switch, the othercontact of said switch being connected to the shield terminal of saidplug, said switch being located in the body of said plug, a resilientactuating member being provided on said body so as to be urged to closesaid switch when said plug is coupled with said jack thereby permittingsaid electric source to be connected to said field effect transistoronly when said plug is coupled with said jack for the operation of thetape recorder.

10. In a microphone device for use with a tape recorder having a remoteswitch jack and a microphone jack, said microphone device including acondenser microphone, a field effect transistor and an electric sourcefor said field effect transistor, the improvement wherein saidmicrophone device comprises a first and a second plug adapted to becoupled with said remote switch jack and said microphone jack,respectively, the center terminal of said first plug being connected tothe minus terminal of said electric source the plug terminal of which isconnected to the drain of said field effect transistor while the gatethereof is connected to one terminal of said microphone the otherterminal of which is connected to the shield terminal of said secondplug, the center terminal thereof being connected to the source of saidfield effect transistor, the shield terminal of said first plug beingconnected to the shield terminal of said second plug, thereby permittingsaid electric source to be connected to said field effect transistoronly when said first and second plugs are coupled with the respectivejacks of the tape recorder.

11. An espionage device, which comprises: a tie clip including a firstelongated member having a serrated surface, a second elongated memberhaving a serrated surface for mating engagement with the serratedsurface of the first member, spring means for biasing said first andsecond members towards each other, the serrated surfaces thereofgripping the tie to which the tie clip is fastened, the other surface ofsaid first member having at least a portion thereof decorativelyembellished;

a first housing mounted to the other surface of said first member, saidhousing including a microphone and amplifying means, connected to saidmicrophone, for amplifying the output thereof, said housing having anaperture in one wall thereof to admit acoustic waves to said microphone,and decorative indicia to disguise said aperture;

a second housing, mounted to the other surface of said second member,and including a source of dc. power for said microphone and amplifyingmeans; and

cable means connecting to said tie clip and invisible when the clip isfastened to a tie, for connecting said power source and said amplifyingmeans one to the other and to an external tape recording device.

12. The espionage device according to claim 11 wherein said first andsecond elongated members are formed from a unitary hairpin shaped memberand said spring means is omitted.

1. In a speaker device for use with a tape recorder having an earphone jack and a remote switch jack for extension connection to an earphone and a remote switch, respectively, said speaker device including a speaker connected to an output circuit therefor, the improvement wherein said speaker device comprises a first and a second plug adapted to be coupled with said remote switch jack and said earphone jack, respectively, the shield terminal of said first plug being connected to the plus side of said output circuit as well as to the center terminal of said first plug, while the earth side of said output circuit is connected to the shield terminal of said second plug, the center terminal thereof being connected to the input terminal of said output circuit, thereby permitting electric power for said output circuit to be supplied from a power source in the tape recorder when said first and said second plug are coupled with the respective jacks for the operation of the tape recorder.
 2. In a speaker device for use with a tape recorder having an earphone jack and a remote switch jack for extension connection to an earphone and a remote switch, respectively, said speaker device including a speaker connected to an output circuit therefor, the improvement wherein said speaker device comprises a first and a second plug adapted to be coupled with said remote switch jack and said earphone jack, respectively, the shield terminal of said first plug being connected to the plus side of said output circuit, while the earth side of said output circuit is connected to the shield terminal of said second plug, the center terminal thereof being connected to the input terminal of said output circuit, a remote switch being connected between the center terminal and the shield terminal of said first plug, thereby permitting electric power for said output circuit to be supplied from a power source in the tape recorder when said first and said second plug are coupled with respective jacks for the operation of the tape recorder while remote control is effected by said remote switch.
 3. In a microphone device for use with a tape recorder having a remote switch jack and a microphone switch jack, said microphone device including a high impedance microphone and a field effect transistor for matching the impedance with the tape recorder, the improvement wherein said microphone device comprises a first and a second plug adapted to be coupled with said remote switch jack and said microphone jack, respectively, the gate of said field effect transistor being connected to said microphone while the drain is connected to the shield terminal of said first plug and the source is connected to the center terminal of said second plug, the shield terminal thereof being connected to said microphone, a remote switch being connected between the center terminal and the shield terminal of said first plug, thereby permitting electric power for said field effect transistor to be supplied from a power source in the tape recorder when said first and said second plug are coupled with the respective jacks for the operation of the tape recorder while remote control is effected by said remote switch.
 4. Microphone device according to claim 3, further comprising a decoupling circuit arranged in the lead wires connecting said plugs to said microphone and said field effect transistor, said remote switch being physically located in a common housing with said decoupling circuit.
 5. Microphone device according to claim 3, further comprising a decoupling circuit arranged integral with said remote switch, said decoupling circuit and said remote switch being connected between the lead wires lead from said microphone and said field effect transistor and from said plugs separately from the lead wires connecting directly said second plug to said microphone as well as said field effect transistor.
 6. In an FM tuner device for use with a tape recorder haviNg remote switch jack and a microphone jack for recording the signal transmitted from a FM transmitter, said FM tuner device including an FM tuner and an antenna connected to said FM tuner, the improvement wherein said FM tuner device comprises a first and a second plug adapted to be coupled with said remote switch jack and said microphone jack, respectively, the plus side of said FM tuner being connected to the center terminal of said first plug which is connected to the shield terminal thereof, while the earth side of said FM tuner is connected to the shield terminal of said second plug, the center terminal thereof being connected to the output terminal of said FM tuner, thereby permitting the electric power for said FM tuner to be supplied from the tape recorder when said first and second plugs are coupled with the respective jacks of the tape recorder operation thereof.
 7. FM tuner device according to claim 6, wherein the tape recorder has a switching circuit and is operable only when said FM tuner receives the signal from the FM transmitter, while said FM tuner is kept in operable position by coupling said first and second plugs with the respective jacks.
 8. In a microphone device for use with a tape recorder having a microphone jack, said microphone device including a condenser microphone, a field effect transistor for accommodating the impedance of the tape recorder with said microphone and an electric source for said field effect transistor, the improvement wherein said microphone device comprises a plug adapted to be coupled with said microphone jack and said electric source is housed in the body of said plug, the center terminal of said plug being connected to the source of said field effect transistor the shield terminal of which is connected to one terminal of said microphone, the other terminal thereof being connected to the gate of said field effect transistor, the plus terminal of said electric source being connected to the drain of said field effect transistor while the minus terminal of said electric source is connected to the shield terminal of said plug, thereby minimizing the size of said microphone device while oscillation thereof is positively prevented.
 9. In a microphone device for use with a tape recorder having a microphone jack, said microphone device including a condenser microphone, a field effect transistor for accommodating the impedance of the tape recorder with said microphone and an electric source for said field effect transistor, the improvement wherein said microphone device comprises a normally opened micro-switch and a plug adapted to be coupled with said microphone device, the center terminal of said plug being connected to the source of said field effect transistor the gate of which is connected to one terminal of said microphone, the other terminal thereof being connected to the shield terminal of said plug, the plug terminal of said electric source being connected to the drain of said field effect transistor, while the minus terminal of said electric source is connected to one contact of said switch, the other contact of said switch being connected to the shield terminal of said plug, said switch being located in the body of said plug, a resilient actuating member being provided on said body so as to be urged to close said switch when said plug is coupled with said jack thereby permitting said electric source to be connected to said field effect transistor only when said plug is coupled with said jack for the operation of the tape recorder.
 10. In a microphone device for use with a tape recorder having a remote switch jack and a microphone jack, said microphone device including a condenser microphone, a field effect transistor and an electric source for said field effect transistor, the improvement wherein said microphone device comprises a first and a second plug adapted to be coupled with said remote switch jack and said microphone jack, respectively, the center terminal of said first plug being connected to the minus terminal of said electric source the plug terminal of which is connected to the drain of said field effect transistor while the gate thereof is connected to one terminal of said microphone the other terminal of which is connected to the shield terminal of said second plug, the center terminal thereof being connected to the source of said field effect transistor, the shield terminal of said first plug being connected to the shield terminal of said second plug, thereby permitting said electric source to be connected to said field effect transistor only when said first and second plugs are coupled with the respective jacks of the tape recorder.
 11. An espionage device, which comprises: a tie clip including a first elongated member having a serrated surface, a second elongated member having a serrated surface for mating engagement with the serrated surface of the first member, spring means for biasing said first and second members towards each other, the serrated surfaces thereof gripping the tie to which the tie clip is fastened, the other surface of said first member having at least a portion thereof decoratively embellished; a first housing mounted to the other surface of said first member, said housing including a microphone and amplifying means, connected to said microphone, for amplifying the output thereof, said housing having an aperture in one wall thereof to admit acoustic waves to said microphone, and decorative indicia to disguise said aperture; a second housing, mounted to the other surface of said second member, and including a source of d.c. power for said microphone and amplifying means; and cable means connecting to said tie clip and invisible when the clip is fastened to a tie, for connecting said power source and said amplifying means one to the other and to an external tape recording device.
 12. The espionage device according to claim 11 wherein said first and second elongated members are formed from a unitary hair-pin shaped member and said spring means is omitted. 